1. Field of the Invention
The present invention relates to method of cleaning a polishing tool used for flattening a variety of films, such as inter-layer insulation films, metal films, and polysilicon films, formed on, for example, a semiconductor wafer by chemical mechanical polishing and a polishing method and polishing apparatus using such a polishing tool.
2. Description of the Related Art
Along with the higher integration and use of multi-layer interconnections of semiconductor devices, the flattening of a variety of films, such as inter-layer insulation film, metal film, and polysilicon film, has become important in the process of production of a semiconductor device. As a technique for the flattening, a variety of means have been proposed, but in recent years, the chemical mechanical polishing (CMP) process is attracting attention, and a polishing apparatus for flattening by utilizing this has been developed.
An example of a polishing apparatus using the conventional CMP process is shown in FIG. 1. A polishing apparatus 301 shown in FIG. 1 has a main shaft spindle 303 for rotating a polishing tool 302 and a rotating table 304 for holding a wafer W. The table 304 is rotatably mounted on a slider 306 provided moveably in an X-axial direction along a rail 305 and rotated by a rotation driving means constituted by, for example, a motor, a pulley, and a belt. The main shaft spindle 303 is held moveably in a Z-axial direction and positioned at a target position in the Z-axial direction by a not illustrated drive mechanism.
In the polishing apparatus 301 having the above constitution, first, the wafer W is rotated at a predetermined speed, and a slurry is continuously fed as an abrasive from a slurry feeder (not illustrated) onto the wafer W. The slurry is obtained by mixing a very fine polishing abrasive, for example, silicon oxide, with a liquid such as an aqueous solution of potassium hydroxide. Next, the polishing tool 302 is rotated at a predetermined speed to position the wafer W and the polishing tool 302 in the X-axial and Z-axial directions so that the polishing tool 302 is located at a position where it contacts an outer circumferential portion of the wafer W. In this state, a surface of the wafer W and a polishing surface of the polishing tool 302 are in substantially a parallel state.
The polishing tool 302 is positioned in the Z-axial direction so as to obtain a predetermined depth of cut with respect to the wafer W. By this, a predetermined polishing pressure is generated between the polishing tool 302 and the wafer W. By movement of the wafer W in the X-axial direction with a predetermined speed pattern and by movement of the contact position between the polishing surface of the polishing tool 302 and the wafer W in this state, the entire surface of the wafer W is polished and the wafer W is flattened.
In the polishing apparatus 301, at the time of discharge of the slurry onto the wafer W and the polishing of the wafer W, the slurry sometimes deposits on the polishing tool 302 and the periphery of its attachment portion and then adheres and solidifies. When the solidified slurry or the like drops from the polishing tool 302 during the polishing and enters into the space between a polished surface of the wafer W and the polishing surface of the polishing tool 302, it acts as a giant abrasive. When polishing pressure is added to the polished surface of the wafer W through the polishing tool 302 and a polishing operation is carried out in this state, it will scratch the polished surface of the wafer W or cause particles to deposit on it. If more than a prescribed number of scratches or residual particles are generated on the polished surface of the wafer W after the polishing, the wafer W ends up becoming a defect.
Further, the polishing tool 302 of the polishing apparatus having the above constitution is formed by an independent foam member, for example, polyurethane foam. The polishing surface of the polishing tool 302 made of such a material is susceptible to a so-called clogged state where the reaction product generated at the time of polishing and the flaked off substance forming the polishing tool 302 enter into the foam member. When in the clogged state, stable polishing cannot be carried out, so it is necessary to dress the tool to remove the surface layer of the polishing surface of the polishing tool 302 in the clogged state to condition the polishing surface of the polishing tool 302. The tool is dressed by shaving the polishing surface of the polishing tool 302 by a dresser with, for example, a diamond abrasive fixed thereto. When dressing the tool, part of the substance constituting the polishing tool 302 flaked from the polishing tool 302 and part of the substance constituting the dresser flaked from the dresser sometimes deposit on the polishing tool 302. The deposited substances sometimes become a cause of scratching the wafer surface.
In order to prevent the scratching of the wafer surface mentioned above, conventionally, for example, pure water was discharged onto the polished surface of the wafer W before the polishing, the polishing tool 302 was moved downward in the Z-axial direction while rotating the same and brought into contact with the pure water layer resident on the wafer W, and the slurry and impurities deposited on the polishing tool 302 were thereby removed to a certain extent.
Further, for example, as shown in FIG. 2, a cleaning use spray nozzle 307 having discharge ports at several positions is disposed in the vicinity of the position just under the polishing tool 302 on the slider 306 moveable in the X-axial direction. The spray nozzle 307 is moved downward up to that vicinity of the polishing tool 302 while rotating immediately before the polishing operation or while standing by for the operation. By cleaning the surface of the polishing tool 302 by discharging pure water from the spray nozzle 307 at a point of time when the polishing tool 302 reaches a predetermined height, the slurry and the impurities deposited on the polishing tool 302 have been removed to a certain extent.
However, there are also cases where they deposit on the outer circumferential surface of the polishing tool 302 or the periphery of the attachment portion of the polishing tool 302 and adhere and solidify. It was difficult to sufficiently remove these solidified impurities by the methods mentioned above or the solidified slurry and impurities deposited on the polishing tool 302 were insufficiently removed in some cases.
Further, there is also a method of disposing a cleaning use brush directly contacting the polishing tool 302 to clean the polishing tool 302, but there is the disadvantage that the solidified slurry and impurities remained inside or outside the cleaning use brush. These solidified slurry and impurities sometimes again are deposited on the polishing tool 302 at the time of the next cleaning and on. Further, if the cleaning use brush is brought into direct contact with the surface of the polishing tool 302, it changes the shape of the polishing surface of the polishing tool 302 or the cleaning use brush gradually deteriorates. Further, it is advantageous for improving the polishing efficiency if an adequate amount of slurry is provided at the surface of the polishing tool 302, but there is also the disadvantage that if the cleaning use brush is brought into direct contact with the surface of the polishing tool 302 to clean the same, even the useful slurry provided at the polishing tool 302 was scraped off.
An object of the present invention is to provide a method for cleaning a polishing tool capable of reliably removing deposited solidified abrasive and impurities.
Another object of the present invention is to provide a polishing method capable of suppressing scratching of a polished object and capable of reducing residual particles on the polished surface of the polished object.
Still another object of the present invention is to provide a polishing apparatus capable of suppressing scratching of a polished object and capable of reducing residual particles on the polished surface of the polished object.
According to one aspect of the present invention, there is provided a cleaning method of a polishing tool for cleaning a rotatably held polishing tool, comprising: arranging with respect to the polishing tool a cleaning member having a facing surface forming a clearance with a cleaned surface of said polishing tool, feeding a cleaning solution to the clearance to form a cleaning solution film, and rotating the polishing tool to clean the cleaned surface.
According to a second aspect of the present invention, there is provided a cleaning method of a polishing tool for cleaning a rotatably held polishing tool, comprising: positioning a correction tool for correcting the polishing surface at a position enabling contact with the polishing surface of the polishing tool, positioning a cleaning member having a facing surface for forming a clearance with at least part of the polishing surface of the polishing tool, feeding a cleaning solution to the clearance to form a cleaning solution film, and rotating the polishing tool to correct the polishing surface while cleaning the cleaned surface.
According to a third aspect of the present invention, there is provided a polishing method for flattening a polished object by making the polishing surface of the rotating polishing tool face the polished surface of the rotating polished object and relatively moving the polished object and the polishing tool along a predetermined plane, comprising: positioning the polishing tool at a predetermined position with respect to a cleaning member provided with a facing surface for forming a clearance with the cleaning face of the polishing tool, feeding a cleaning solution to the clearance formed between the facing surface and the cleaned surface to form a cleaning solution film, rotating the polishing tool to clean the cleaned surface and polishing the polished object by using the cleaned polishing tool.
According to a fourth aspect of the present invention, there is provided a polishing apparatus comprising: a polishing means for flattening a polished object by a rotating polishing tool and a polishing tool cleaning means for cleaning the surface of the polishing tool, wherein the polishing tool cleaning means has a cleaning member having a facing surface for forming a clearance for forming a film of a cleaning solution with the cleaned surface of the rotating polishing tool and a cleaning solution feeding means for feeding the cleaning solution to the clearance. In the present invention, when the cleaning solution is fed to the clearance formed between the cleaned surface of the polishing tool and the facing surface of the cleaning use member, a film of the cleaning solution is formed between the cleaned surface and the facing surface. When the polishing tool is rotated in this state, the cleaned surface of the polishing tool and the facing surface of the cleaning use member relatively move, a shearing force acts upon the film of the cleaning solution due to the resistance between the cleaned surface of the polishing tool and the facing surface of the cleaning use member, and the shearing force acting upon this film of cleaning solution removes the solidified abrasive and impurities deposited on the cleaned surface of the polishing tool with a high efficiency. Further, by making the facing surface of the cleaning use member partially face the cleaned surface of the polishing tool, the solidified abrasive and impurities removed from the cleaned surface of the polishing tool and contained in the cleaning solution are discharged to the outside together with the cleaning solution from the clearance formed between the cleaned surface of the polishing tool and the facing surface of the cleaning use member and will not deposit again to the cleaned surface of the polishing tool. Further, in the present invention, by simultaneously correcting the polishing surface of the polishing tool by the correction tool together with the cleaning of the polishing tool, the cleaning solution deposited on the polishing surface of the polishing tool also cleans the correction tool. Further, in the present invention, by feeding the cleaning solution to the clearance formed between the cleaned surface of the polishing tool and the facing surface of the cleaning use member through the feed ports formed in the facing surface of the cleaning use member, a sufficient amount of the cleaning solution is stably fed to the clearance formed between the cleaned surface of the polishing tool and the facing surface of the cleaning use member and the film of the cleaning solution is stably formed.